I. Field of the Invention
This invention relates generally to air-accumulator and discharge devices of the type generally known as air blasters, air cannons, or blast aerators. More particularly, the present invention relates to heavy duty blast aerators of the type classified in United States Patent Class 222, Subclasses 2, 3 and 195 and Class 251, Subclass 30.02.
II. Description of the Prior Art
As is well known to those with skill in the art, the passage of bulk materials through conventional handling equipment is often degraded or interrupted. Typical bulk materials comprise concrete mixtures, grains, wood chips or other granular materials disposed within large hoppers or storage bins. In conventional, conically shaped hoppers, for example, bridges or arches of bulk materials often form, preventing or minimizing the orderly flow or delivery of granular materials. Often, xe2x80x9crat holesxe2x80x9d or funnels build up, and material passage is severely degraded or halted altogether. Particles of bulk material may form obstructive bonds by adhesion due to chemical or hydrostatic attraction. Particles may also interlock because of horizontal and vertical compression. Such materials usually tend to cake or congeal during bulk processing. When moisture accumulates, unwanted caking tends to block flow. It is also recognized that friction between bulk material and the walls of a typical bunker or hopper in which the material is confined decreases flow efficiency.
Blast aerators or air cannons have long been employed to dislodge blocked or jammed bulk material. Storage bins or hoppers, for example, are often fitted with one or more high pressure air cannons that periodically blast air into the interior to dislodge caked particles, break funnels and bridges, and destroy rat holes. Bulk flow problems can temporarily be stopped by physically vibrating the hopper or container to shake loose the jammed materials. But not all materials may be dislodged in this manner. For example, large concrete bunkers may be impossible to vibrate. Materials like soft wood chips ordinarily absorb vibratory energy and must be dislodged by other methods.
In many applications air blasters are preferred over vibrators because of efficiency. The forces outputted by blast aerators are applied directly to the material to be dislodged, rather than to the walls of the structure. Modern air blasters usually outperform over air slides, air wands, and various air screen devices which operate at low pressures. Live bottoms in hoppers or bins are limited in their effectiveness, since they may tend to create bridging or arching of material. Modern air cannons or blast aerators are intended for use as a flow stimulator against materials that are primarily moved by gravity. They are not intended to be the prime movers of such materials, and for safety purposes they should not be used to initiate the flow or movement of bulk materials unless a gravity feed is employed.
Typical blast aerators comprise a large, rigid holding tank that relatively slowly accumulates air supplied through conventional high pressure air lines provided at typical industrial facilities. A special valve assembly associated with the tank includes a high volume discharge opening directed towards or within the target application. The valve assembly periodically activates the air cannon in response to a trigger. When the blaster is detonated, the large volume of air accumulated in the holding tank is rapidly, forcibly discharged within a few milliseconds. Compressed air released by a modern blast aerator strikes the bulk material at a rate of between five hundred feet per second to eight hundred feet per second. Materials exposed to this high volume inrush are forcibly dislodged by impact. The large volume of air outputted by the aerator spreads throughout the bin or hopper, distributing forces throughout the interior that tend to homogenize and dislodge the mixture. The impacting shock wave rapidly destroys any formations of bulk material that might otherwise hinder fluid flow.
After an exhaust blast, the valve apparatus returns to a xe2x80x9cfillxe2x80x9d position, wherein an internal, displaceable piston typically blocks the aerator blast output path. The cycle repeats as air that has relatively slowly accumulated again within the blaster is subsequently discharged during the next cycle. A variety of methods have been proposed for controlling the aerator valve assemblies. Various means such as electrical solenoids have been provided for allowing or forcing the discharge piston to rapidly retreat from its normally sealed, blocking position abutting the discharge valve passageways.
U.S. Pat. No. 4,469,247, issued Sep. 4, 1984, and owned by Global Manufacturing Inc., discloses a blast aerator for dislodging bulk materials. The blast aerator tank has a blast discharge opening coaxially aligned with its longitudinal axis. The blast discharge assembly comprises a rigid, tubular discharge pipe comprising an internal shoulder that forms a valve seat. A resilient piston coaxially, slidably disposed within the pipe abuts the valve seat to seal the tank during the fill cycle. In the fill position the seal is maintained by a chamfered end of the piston that matingly, sealingly contacts a similarly chamfered seat portion of the valve seat assembly. A cavity at the piston rear is pressurized to close the valve by deflecting the piston. During periodic cycles, discharge occurs in response to cavity venting, whereupon the piston is rapidly displaced away from the valve seat, exposing the discharge pipe opening to the pressurized tank interior.
Blast aerators characterized by the foregoing generalized structure may be seen in U.S. Pat. Nos. 3,651,988; 3,915,339; 4,197,966; 4,346,822; and 5,143,256. Other relevant blast aerator technology may be seen in Great Britain Pat. Nos. 1,426,035 and 1,454,261. Also relevant are West German Patent 2,402,001 and Australian Pat. No. 175,551.
Global Manufacturing patent No. 4,496,076 teaches a method of employing a plurality of air cannons in a controlled array.
In some prior art aerator designs, the piston and valve assembly are disposed at a right angle relative to the discharge flow path. In addition, many blast aerators use a valve assembly that is mounted externally of the accumulator tank. The latter design features are seen in U.S. Pat. Nos. 3,942,684; 4,767,024; 4,826,051; 4,817,821; and 5,853,160.
During the hundreds of thousands of repetitive discharge cycles occurring over the normal life of a typical blast aerator, critical moving parts will inevitably wear and deform. Typical pistons encounter extremely high stresses from heat, friction, and pressure that eventually result in component failure. For example, as the piston deforms or wears, its ability to properly seal during the critical xe2x80x9cfill cyclexe2x80x9d is impaired. In many prior art designs that portion of the piston utilized to create a seal also functions as the working surface upon which tank pressure acts to force the piston to its rearward xe2x80x9cblastxe2x80x9d position, further aggravating component stress and shortening valve life. In operation, the piston must rapidly travel away from the seal during the discharge cycle. As it deforms over hundreds of thousands of blast cycles however, it may lose its symmetry, and misalignment within the valve tube can slow piston travel, enlarging the blast time period and denigrating the force of the discharge. When critical structural parts fail, injury to operating personnel may occur. At the very least, aerator component breakdown may severely limit bulk flow efficiency. Therefore some form of dynamic control over the piston that limits stress would seem desirable. Some attempts in this direction are acknowledged.
U.S. Pat. No. 5,441,171 discloses a protrusion on the rear of a slidably captivated piston to help slow the piston after firing. This design does not bleed air off in a controlled fashion and in fact the protrusion does not shut off the flow of air out of the valve body.
U.S. Pat. No. 5,517,898 discloses a pneumatic cylinder in which coaxially disposed xe2x80x9cpistonsxe2x80x9d include dampening sleeves. In other words, ports are interconnected with internal passageways including stem portions of the cylinder to dampen piston movement by compressed air.
The actuator system disclosed in my prior U.S. Pat. No. 6,321,939 that was issued Nov. 27, 2001, includes a dampened, high-speed actuator. A unique, lightweight piston within the actuator is controlled through a dampening arrangement that mitigates piston shock. Special structure protruding from the piston is received within a passageway end cap when the piston is retracted during firing, and special vents govern the rate of air flow and pneumatic equilibrium. Cushioning pressures at the rear of the piston dampen piston movement. A coiled metal spring between the piston and the housing end cap provides additional cushioning.
During firing the spring is compressed at a very rapid rate as the piton retracts. Full compression occurs in approximately 0.01 seconds. Corresponding piston velocity for an aerator with a typical four inch O. D. actuator output pipe is approximately 200 to 250 feet per second. After repetitive cycles at such speeds, the coiled spring may fail, especially in high temperature applications. Spring problems are recognized in the aerator industry with many designs. The coils of the spring are compressed together during firing, generating heat and slowing the piston. This phenomenon degrades the output forces achievable by the air blaster. spring adds cost to the Air Blaster.
It is therefore proposed to provide a xe2x80x9cspring-lessxe2x80x9d air blaster. In other words, separate mechanical springs are omitted from the new design. Instead of a mechanical spring, pneumatic forces are employed for cushioning and dampening. In this xe2x80x9cpneumatic designxe2x80x9d the actuator valve assembly is controlled by a special trigger. In other words, standard, electrically-operated pneumatic trigger valves have been replaced by my xe2x80x9cquick exhaust valvexe2x80x9d described in provisional application Serial No. 60/350,250. The actuator system disclosed in prior U.S. Pat. No. 6,321,939 has been modified as described below, and when coupled to the new quick exhaust valve, piston travel and dampening are mitigated by pneumatic forces in the trigger arrangement.
A blast aerator system with a xe2x80x9cspring-lessxe2x80x9d actuator is triggered by a special quick exhaust valve. The rigid holding tank mounts the actuator at it""s discharge end, and the exhaust valve trigger is secured to the opposite end, being coupled to the actuator through an internal pipe coaxially extending through the tank.
The preferred valve assembly includes an internal, slidably mounted piston that normally blocks the exhaust path (i.e., during tank filling). The piston normally contacts an internal valve seat, but when deflected away the exhaust vents are suddenly exposed and discharge occurs. In the high temperature mode, the piston is heat resistant. It is preferably made of 6061-T6 aluminum. The low temperature piston is made from resilient material such as polypropylene. A rigid valve cap closes the valve actuator assembly. The valve cap comprises an upper, dome-like portion and an integral, lower disk portion coaxially fitted to the actuator body. The piston comprises a generally cylindrical dampener that is received within a dampener passageway in the end cap.
The trigger at the opposite end of the tank comprises a symmetrical, ventilated housing that mounts a miniature, hollow, lightweight piston. A plurality of vent orifices radially disposed about the housing periphery, are normally covered by a pair of resilient bands that may be deflected away from the orifices in response to sufficient air pressure, thus functioning as a check valve. The captivated, generally cylindrical piston is lightweight and hollow. An air passageway extending through the trigger piston is controlled by a deflectable ball forming a valve element. The spherical check valve is captivated within a tapered chamber inside the piston for selectively blocking and exposing various air passages through the piston as it contacts or separates itself from an internal valve seat.
The actuator valve assembly and trigger valve assembly are in fluid flow communication. Trapped residual air within the trigger valve serves as a pneumatic spring to resist and dampen movement of the actuator valve piston. The actuator valve piston is effectively cushioned pneumatically by the trigger valve assembly, eliminating the requirement for a separate mechanical spring. Because there is no a need to machine a spring groove in the piston, piston weight and mass can be reduced; the preferred hollow actuator piston is thus capable of faster movements.
Thus a basic object of this invention is to provide a blast aerator with a spring-less actuator valve.
A related object is to provide a blast aerator with a high speed trigger mechanism that obviates the need for mechanical springs in the associated actuator valve assembly.
Another basic object is to provide a highly reliable blast aerator that resists high temperatures and mechanical stresses.
Another object is to provide a blast aerator trigger of the character described that is of minimal volume and weight.
A fundamental object is to provide a highly reliable blast aerator.
A still further object is to speed up the blast aerator charging and discharging cycle.
A still further basic object is to provide a blast aerator trigger of the character described that minimizes the number of required service calls.
A related object is to control piston deterioration by pneumatically cushioning and controlling it during blast discharges.
Another general object of this invention is to provide a pneumatically dampened piston and valve assembly that extends the useful life of the aerator.
A still further object is to further improve the aerator designs of my prior U.S. Pat. No. 6,321,939.
These and other objects and advantages of this invention, long with features of novelty appurtenant thereto, will appear or become apparent in the course of the following descriptive sections.